1. Field of the Invention
The present invention relates to a method for joining tube headers and header tanks of a heat exchanger, and more particularly to a method for joining tube headers and header tanks of a heat exchanger made of a plastic material by joining fin-tube units of a fin-tube assembly with tube headers in accordance with a thermal fusing method while joining the fin-tube units with each header tank in accordance with a fusing method using ultrasonic waves.
2. Description of the Prior Art
Referring to FIG. 1, a heat exchanger used for an evaporator included in a conventional refrigerator is illustrated. As shown in FIG. 1, the heat exchanger includes a metallic refrigerant tube 1 including a refrigerant inlet tube section 2 and a refrigerant outlet tube section 3. Fins 4 are formed on the periphery of the refrigerant tube 1 along the length of the refrigerant tube 1. A left header (not shown) and a right header 6, which are made of metal, are joined to opposite lateral ends of a zigzag-shaped tube structure formed by the refrigerant tube 1, respectively. Also, defrosting tubes 7 are arranged at the opposite lateral ends of the zigzag-shaped tube structure, respectively.
Now, the conventional heat exchanger having the above mentioned arrangement will be described in brief.
A refrigerant is introduced into the refrigerant tube 1 via the refrigerant inlet section 2 corresponding to the inlet of an evaporator. The refrigerant passes through a zigzag-shaped refrigerant path defined in the refrigerant tube 1, and then reaches the refrigerant outlet tube section 3. The refrigerant is subjected to an evaporation process while passing though the refrigerant tube 1. During the evaporation process, the refrigerant conducts heat exchange based on exchange between latent heat and sensible heat. The refrigerant emerging from the refrigerant outlet tube section 3 is then introduced into an accumulator 8. The accumulator 8 functions as a refrigerant storage tank coping with a variation in load depending on the surroundings around the associated refrigerator while functioning as a moisture-liquid separator. The defrosting tubes 7 have to periodically defrost ice attached to the surface of the evaporator. For this reason, electrical heating type heaters are used for the defrosting tubes 7. The tip of each fin is substantially in linear contact with an associated one of the defrosting tubes 7.
FIGS. 2 and 3 illustrate another heat exchanger used for an evaporator included in a conventional refrigerator, respectively. The illustrated heat exchanger is a tri-tube evaporator in which a refrigerant tube, fins, and defrosting tubes are integral together.
As shown in FIGS. 2 and 3, fins 12 are formed on the periphery of a metallic refrigerant tube 11 along the length of the metallic refrigerant tube 11. A defrosting tube 13 is formed at the periphery of each fin 12.
A refrigerant is introduced into the evaporator at a left end of the evaporator via the left end of a tri-tube 10. The refrigerant passes through the tri-tube 10 defining a zigzag-shaped refrigerant path, and then emerges from the evaporator via an accumulator 15 arranged at the outlet of a refrigerant tube 14 connected to the right end of the tri-tube 10.
As apparent from the above description, conventional fin-tube type evaporators have a structure in which fins 12 are coupled to the metallic refrigerant tube 11 in accordance with a diameter enlargement of the metallic refrigerant tube 11. In particular, the accumulator 15 is joined to the outlet of the refrigerant tube 11 by means of welding. For this reason, noise is generated when the refrigerator is turned on and off. Moreover, such a conventional joining method cannot be applied to heat exchangers made of a plastic material, as in the present invention.
Therefore, the present invention has been made in view of the above mentioned problems, and an object of the invention is to provide a method for joining tube headers and header tanks of a heat exchanger made of a plastic material by bring the tube headers and header tanks into contact with associated fin-tube units of a fin-tube assembly, pressing the tube headers and header tanks against the associated fin-tube units by a thermal fusing machine, thereby thermally fusing the tube headers and header tanks to the associated fin-tube units.
In accordance with one aspect, the present invention provides a method for joining tube headers of a plastic heat exchanger, comprising the steps of: forming fins of a plastic material on respective outer peripheral surfaces of refrigerant tubes made of a plastic material and arranged in a laminated fashion while allowing each of the fins to connect associated adjacent ones of the refrigerant tubes, thereby forming a fin-tube assembly having a plurality of fin-tube units each consisting of one refrigerant tube and one fin; forming tube headers of a plastic material at opposite ends of each of the fin-tube units in accordance with a double injection molding process, respectively; arranging a thermal fusing jig to support respective bottoms of the tube headers at each end of the fin-tube assembly; and pressing thermal fusing molding dies of a thermal fusing machine against the fin-tube units at each end of the fin-tube assembly, thereby thermally fusing the tube headers to the fin-tube units, so that the tube headers are integral with the fin-tube units, respectively.
Each of the thermal fusing molding dies may have an inverted-triangular cross-sectional shape.
The step of thermally fusing the tube headers to the fin-tube units may be carried out under a condition, in which respective portions of the tube headers and fin-tube units being thermally fused are maintained at a temperature of 300 to 320xc2x0 C., until respective portions of the tube headers and fin-tube units being thermally fused exhibit a thickness reduction of 50%.
In accordance with another aspect, the present invention provides a method for joining tube headers of a plastic heat exchanger, comprising the steps of: forming fins of a plastic material on respective outer peripheral surfaces of refrigerant tubes made of a plastic material and arranged in a laminated fashion while allowing each of the fins to connect associated adjacent ones of the refrigerant tubes, thereby forming a fin-tube assembly having a plurality of fin-tube units each consisting of one refrigerant tube and one fin; forming tube headers at opposite ends of each of the fin-tube units in accordance with a double injection molding process, respectively; arranging header tanks of a plastic material at opposite ends of the fin-tube assembly while bringing each of the header tanks into contact with the tube headers arranged at an associated one of the opposite ends of the fin-tube assembly; and arranging a heat generating device on each of the header tanks, and thermally fusing the header tank to the tube headers arranged at the associated end of the fin-tube assembly in accordance with an operation of the heat generating device.
The heat generating device may be a piezoelectric device.
Preferably, the piezoelectric device generates vibrations having mechanical vertical vibration energy of 15,000/sec and an exciting amplitude of 0.06 to 0.08 mm (pxe2x80x94p: peak to peak).
The present invention has features in that respective materials of elements in the heat exchanger are plastic materials, and that pins and refrigerant tubes of the heat exchanger are integrally formed in accordance with a plastic extrusion process. In accordance with such features, the present invention provides a method for joining tube headers of a plastic heat exchanger by overlapping tube headers with respective ends of tubes being extruded, and applying heat to the overlapped portions. Also, the present invention provides a method for joining the tube headers to a header tank, in accordance with a thermal fusing process using ultrasonic waves.